Method of etching printing-plates.



ivo. 764,082.

patented .my 5, 1904.

PATENT OFFICE.

WILLARD G. THORPE, OF LOS ANGELES, CALIFORNIA.

METHOD OF ETCHING PRINTING-PLATES.

SPECIFICATION forming part of Letters Patent No. 764,082, dated July 5,1904.

Application filed March 8, 1904. Serial No. 197,067. (No model.)

To all whom, zit may concern,.-

Be it known that I, IILLARD G. THORPE, a citizen of the United States,residing' at Los Angeles, in the county of Los Angeles and State ofCalifornia, have invented a new and useful Method of EtchingPrinting-Plates, of which the following is a specification.

The primary object of my invention is to etch zinc or other metal platesexpeditiously and in such manner as to produce the maximum sharpness andclearness of the design.

Another object of my invention is to subject the plate to the scouringor cleaning action of an etching agent directed perpendicularly thereto,so as to continually remove deposits therefrom and maintain the etchingaction, giving' superior sharpness and clearness of design Without theuse of an air-blast.

A further object of the invention is to subject the plate to such actionwhile it is placed face uppermost, so as to allow inspection of I theprogress of the work without having to overturn the plate.

In etching zinc plates the corrosion by the etching uid forms a depositor scale on the exposed parts of the plate, and this deposit interfereswith the further action of the etching agent.` It is usual to removethis deposit from time to time by the use of a brush, so as to enablethe etching process to proceed. This brushing action is injurious to thedesign formed on the plate, as it tends to scratch the lines and wearaway the liner details and the edges of resist parts of the design.

My invention provides for continual removal of the deposit by themechanical action of the etching agent itself. I am aware that it hasbeen proposed to effect this result by the action of an atomized spraydirected against the plate from below, the plate being placed with thedesign downward.

According to my method the plate is placed substantially horizontal,design-face uppermost, and the etching fluid is allowed to fall ontosaid face by the action of gravity. I prefer to apply the Huid in theform of a rain --that is, a multiplicity of falling drops of sufcientsize to fall freely with little retardation by the resistance of theair-in distinction to an atomized spray which requires a current orblast of air to direct it against the plate.

In the accompanying draWings,Figure l represents diagrammatieally anapparatus suitable for carrying out my invention. Fig. 2 is an enlargedvertical section of a part of the plate, showing the action of the Huidin striking same.

It will be understood that the invention mayl cated above the support 2and provided with l openings ,4, adapted to allow the fluid from thereservoir to pass downward in drops or rain onto the plate below. A tankor reservoir 5 is arranged below and around the support 2 to receive theuid iowing from the surface of the plate. Means are provided forreturning the iiuid from tank 5 to distributer 3, such means,consisting, for example, of a pump 6, driven by amotorand communicatingwith the reservoir 5 and with a pipe 8, leading to the distributer 3.

It being desirable to impart to the fluid a limited amount of horizontalmovement to insure its even distribution o'n the surface of the plate,the tank 3 is supported by swinging supports 9, so as to be horizontallymovable. This movement may be imparted by any suitable means-forexample, by hand; but a convenient means is that shown, consisting of adasher l0 on the distributer in the path of the discharge from pipe 8,so as to be jarred by the impact of the fluid. In carrying out theprocess in this apparatus the plate 1,which has been suitably preparedwith portions of its face 11 covered by a resist corresponding to thedesign, is placed with the face 11 uppermost on the support 2, and themotor 7 being set in operation the etching fluid is pumped up from tank5 into tank or distributer 3, whence it issues in the form of drops orrain, (indicated at 12,) falling in approxi- IOO however, is notsufficient to interfere with thev substantially perpendicular impact ofthe drops on the design-surface. The mechanical action of the fluid onthe plate is illustrated in Fig. 2, the drops striking the plate with ysuch force and velocity that the deposits formed by the etching actionon all parts of the plate not covered by the design are broken up anddislodged or forcibly detached from the plate by the impact of thefluid, and the splashing and scouring action due to the rebound of thefluid completes the separation of the deposit and allows the same to bewashed away by the fluid. The effect of such perpendicular impactdiffers from that of the usual rocking horizontal movement of theetching fluid in the following' respects: It exerts a more powerfulscouring action due to the forcible impact of the drops on the surface.It attacks all parts of the exposed surface of the design equally,whereas the horizontalmovement produces less effect where the exposedparts are of small extent or already etched below the general surface,the relief of the surrounding parts protecting such depressed parts fromthe wash of the fluid. There is less danger of overetching of smalldetails or lines, as the perpendicularly-moving fluid does not tend towash away the edges of the resist or to undermine the same as does ahorizontal wash. There is less danger of underetching of large masses ordesign portions, as the uid cuts clean and sharp at the edge of theresist, whereas with a horizontal movement the parts immediatelyadjacent a heavy resist are protected more or less from the cutting'action of the Huid.

Fig. 2 illustrates the above-described action,

13 indicating a small resist portion whose edges are suscept1ble toinjury or wear by the -wash of the fluid, and 14 indicating a largeresist portion, which protects the adjacent portions 15 of the platefrom the wash of the fluid.

What I claim is- 1. The method of etching a plate on a face of whichadesign has been formed by a resist, which consists in subjecting theplate with the design-face uppermost, to the action of etching fluidfalling upon the design-face with sufficient velocity to dislodge andremove the deposits thereon.

2. The method of etching a plate having a design formed on a facethereof by a resist which consists in subjecting the plate, with thedesign-face uppermost, to the action of a rain of etching fluid, fallingperpendicularly against the design-surface with sufhcient velocity todislodge and remove deposits thereon.

3. The method of etching a plate having a design formed on afaccthereof, which consists in placing the plate with thc design-faceuppermost and allowing the etching fluid to fall perpendicularly uponthe design -face by distributed series of drops with sufficient velocityto dislodge and remove deposits thereon, and changing the horizontalposition of such series of drops.

1 1. The method of removing the deposit from a plate having a resistover a portion thereof in the process of etching, which consists inallowing the etching fluid to fall against the surface of said platewith sufficient violence to dislodge said deposit.

1n testimony whereof I have signed my name to this specification, in thepresence of two subscribing witnesses, at Los Angeles, in the county ofLos Angeles and State of California, this Qd day of March, 1904.

ll/VILLARD G'. THORPE. 1n presence of- JULIA ToWNsEND,

ARTHUR P. KNIGHT.

